Roof deck structure having a continuous vapor barrier and composite insulating element therefor



3,079, 730 BARRIER THEREFOR J. W. DONEGAN ROOF DECK STRUCTURE HAVING A CONTINUOUS VAPOR AND COMPOSITE INSULATING ELEMENT Filed March 4, 1958 March 5, 1963 INVENTOR JOSEPH W. DON EGAN ATTORNEY 9 J FA '3 F7 E 5i Fatented Mar. 5, i953 tinuity of the vapor barrier is not sustained becaused the 3,679,7 8 vapor barrier film is substantially below the tongue and B32132; HAVEFJG A C SNlZN- Joseph W. Donegan, Leonie, Ni, esslgnor to Allied Qhernical & Dye Qorporation, New York, N32, a corporation of New York Filed 4, 1953, Ser. No. 76 ,151 2 Claims. (Cl. 5ti-346) This invention relates to an insulating structure having a continuous vapor barrier, and to a composite insulating construction element therefor.

Insulating roof deck elements or units are currently beiru produced having vapor barrier sheets or films for preventing passage of water vapor across the barrier and into the interior of the insulating material on the other side thereof. T he elements typically each comprise superposed fibrous insulating boards, and a vapor barrier sheet or film intermediate and bonding the boards. The elements typically have tongued and grooved edges and are assembled or joined through tongue and groove joints to form the roof deck.

While the roof deck elem nts above mentioned provide an effective vapor barrier within each element, the barrier is usually discontinuous or not connected in the joints of adjoining elements. Consequently, moisturecontaining or humid air tends to pass upwardly through the discontinuity or space between the non-connected,

barrier sheets or films and into the interior or" the upper insulating board. By reason of the typical indoor temperatures and relative humidities employed in homes throughout a considerable part of the country during the winter, e.g. 70 F. and 30% respectively, and the relatively low or below freezing outdoor temperature, e.g. F., a dew point temperature tends to exist (for the existing humidity conditions) within the roof deck structure at a location or level thereof not a great distance above the vapor barrier. Consequently, condensation of moisture from the air will occur at the plane or location of the dew point temperature with resultant deposition of water in the insulating material. Such water deposition is highly undesirable inasmuch as loss of insulating value, deterioration of fibrous insulating boards, blistering or" paint from decorative surfaces, etc, is not infrequently attendmt therewith. Furthermore, the absorption of moisturecontaining air from within the building due to the vapor barrier discontinuity may promote formation of roof blisters. Under solar heat, the moisture saturated air within the insulation expands greatly, producing the gas volumes and pressures which produce blisters in the roof. Additionally, the moisture within the insulating materifl is subject to freezing in severe cold weather, and the frozen water may cause fracturing in portions of the roof due to expansive forces exerted thereby.

Prior art efiorts to provide continuity of vapor barrier through joints of contiguous roof deck elements have, in general, produced unsatisfactory results. For instance, in one insulating roof deck element of the type previously mentioned, a rubber gasket is disposed on the long edge of the element immediately below its tongue and a substantial distance above the exposed edge of the vapor barrier film not in contact therewith. Upon assemblage of the elements through tongue and groove joints at longitudinal edges, the vapor barrier is discontinuous between adjoining elements because the gasket is above the vapor barrier edges and not in contact with these edges. in another roof deck element of the aforementioned type having its vapor barrier film substantially below its tongue, the tongue and groove joint obtained by assemblage or engagement of this element with another similar element is caulked with a caulking compound. However, connot within the joint. Consequently, leakage or passage of moisture-containing or humid air through each discontinuity or space between the non-connected vapor barriers of these prior art roof decks may occur with the attend ant aforementioned undesirable results.

It is therefore an object of this invention to provide an insulating structure such as a roof deck structure having a continuous and sealed vapor barrier between adjoining vapor barrier-providing insulating elements or units thereof, which continuous and sealed barrier will prevent passage of vapor from one side of the barrier to the other side thereof and into the interior structure of the insulating material with the aforementioned undesirable results.

Another object is to provide a composite tongued and grooved insulating construction element or unit, such as an insulating roof deck unit, having both a vapor barrier and a strip of vapor impervious material installed or bonded in the groove thereof, which strip is adapted, on joining or engagement of the units, to provide a continuous and sealed vapor barrier between adjoining units thereby preventing the aforementioned undesirable results.

Additional objects and advantages will be apparent as the invention is hereinafter described in detail.

It has now been found that a continuous and sealed vapor barrier between adjoining composite vapor barrierproviding insulating elements or units, which units are joined or engaged edge to edge through tongue and groove joints in an insulating structure, is achieved by means of a strip of vapor impervious material disposed in the groove of the joint or joints between adjoining units. The vapor impervious strip is located or disposed in the joint groove in such a manner as to contact and connect vapor impervious film edges or adjoining units within the joint thereby forming a continuous and sealed vapor barrier between adjoining units. Consequently, passage or transmission of vapor into the interior structure of the insulating material on the other side of the joint with the attendant aforementioned undesirable results is prevented.

Any water vapor impervious or substantially impervious material capable of forming a vapor tight seal with exposed vapor impervious film edges of adjoining insulating units, can be utilized for formation of the vapor barrier-continuity providing strip. Examples of preferred material for formation of the strip include any permanently adhesive materials which are water vapor impervious, or substantially impervious, e.g., a permanently adhesive and plastic composition comprising, by weight, chlorinated rubber 2545%, Cumar resin 3055% and dibutyl phthalate (as plasticizer) 10-25%; rubberized asphalt or pitch. Non-adhesive, deformable or compressible water vapor impervious or substantially impervious materials, e.g. rubber, polyurethane, or polyvinyl chloride, as soft compounds or as foams, are also well suited for formation of the strip. The foregoing preferred and well suited materials are characterized by being non-flowable at normal indoor or outdoor summer temperatures and by being non-brittle at normal outdoor winter temperatures. Other less preferred materials for forming the strip are asphalt or coal'tar pitch, and asphalt-rubber or pitch-rubber compounds. When asphalt or pitch are employed, it may be necessary to render the surface thereof which will contact the vapor barrier film edge sticky or tacky (for sealing) by application of a suitable solvent, such as solvent naphtha, or by application of heat. The Cumar resin of the aforementioned plasticized chlorinated rubber composition is a paracouma-rone-indene resin available in commerce. By the term permanently adhesive as applied to preferred aforementioned adhesive vapor impervious materials is meant a vapor impervious material-which will retain its stickiness or adhesiveness'.

3 (in addition to its water vapor imperviousness) over a lasting or prolonged time period, typically of at least 2 years.

The tongue and groove joints-betweenadjoininginsulating units'are preferably so designed as to combine insured smooth or even alignment of the interior exposed.

decorative surfaces of the units with tight joints andease of assembly or joining thereof. In accordance with this.

because the groove of each unit has. greater widthat its.

mouth or entrance thereto than at its bottom, insertion of a unit tongue thjereinto is facilitated.

Inthe'preferred roof deck structure, a vent channel is located in the base 'or-bottom of the groove ofeach insulating unit. The channel, which isispacedfrom the exposed film edge in the groove bottom, communicates with similar vent channels in adjoining units to facilitate venting any destructive pressures built up withinthe units;

thereby preventing distorting or blistering of superimposed roofing. Quick and ready venting of destructive pressures is important for thereason that the porous insulating material of the roof deck units contain considerable quantities'of air within their internal structure. Upon'exposure of the roof to direct sunlightsuch as during the summer months, the air (which contains some water. vapor) expands and substantialgas pressures tendto-be generated in theinsulating material of' the roofdeck units. If these destructive pressures are;notfr eleased or vented from the insulating material, the aforementioned. distorting or blistering of the roofing material may occur.

In the drawings:

FIGURE 1 is a-fragmentary elevational sectionalview of an insulating roofgdeck' structure of this invention having a sealed and. continuous vapor barrier between individual vapor barrier-providing units makingup the roof deck, which roof. deck has conventionalroofing thereon. FIGURE '2' is atop plan viewof a tongued and grooved vapor barrier-providing insulating unit.

FIGURE 3 isasection on.line 33 of FIGURE 2 showing a vapor impervious. strip installed in the groove bottom of an insulating unit contacting and covering a normally exposed edge of'a vapor impervious film;

FIGURE 4is a fragmentary elevational sectional view of a pair-of engaged vapor. barrier-providing insulating roof deck units having conventional roofing thereon, and providedwith sealed vapor barrier continuity between the unitsaccording to another embodiment of. the invention.

FIGURE 5 is a fragmentary top-plan view of tongued and grooved vapor-barrier providing insulating units engaged edge to edge throughtongue. and groove joints, which view also'shows vent channels in the engaged units in communication with each'other.

Referring to FIGURE 1, compositeinsulating. elements or units are joined or engaged edge to edge through tongue and groove jointst-to form a roof deck structure,- each unit comprising upper'insulating board 11, relatively thin lower insulating boardillproviding an interior exposed decorative surfacejl3 (typically a painted surface), andcontinuousfilm l t ofwater vapor impervious material, exn' asphalt,.extending between and coextensive with and bonding the boards. The roof deck is supportedby spaced-rafters or cross: beams (not shown). A fillet 'or strip 'of the plasticized chlorinated rubber composition or other vapor impervious material previously mentioned is-bonded-in the lower corner of each joint groove. As

shown, each tongue terminates short of each groove bottom. The strip extends the length of the groove and" covers and connects normally exposed film edges 16 and 17 at a lower level of groove bottom 18 and of leading tongue edge 19, respectively. Consequently, a continuous and sealed vapor barrier is provided between the units. The vapor impervious'film 14 and vapor barrier continuity-providing strip 15 are preferably located in a lower portion or level of the roof deck and of each tongue and: groove joint'thereof, to insure presence of the vapor barrier below the location or plane of the dew .point temperature.

The tongue of each insulating unithas horizontal, parallel, opposite faces 20 and 21 respectively. The groove of each adjoining unit has horizontal lower face 22 and upper face 23 inclined upwardly and outwardly of the unit. Consequently, upper face 23 of 'eachgroove" exerts force or pinches against each tongue edge 24 resulting in edge faces 2Sand26 beloW-the-tongue and groove respectively of the adjoining units bearing'orabut ting firmly againstoneanother, to achieve smooth or even alignment of the exposed 'decorativesurfaces thereof. As-shown, edge27 of each unit above the tongue islocated more rearwardjof the unit' relative to-its'tongue than, edge. face. 25" below the tongue to provide clearance for attainment of the even alignmentofthedecorativesurfaces above discussed.

Ventehannel. 28,- of. lesser width than the groove bottom, is. locatedjn the groove bottom i each. insulating unit. They channel communicates with similar ventchannels in adjoining units. to vent to the atmosphere any destructive pressures. built upwithin the insulating material of the units. Consequently, blistering orv distorting of superimposed conventional roofing29 is prevented; Roofing 29 may comprise conventional builtuproofingofcoal tar pitch and tar-saturated felt, or other roofing well known in .the art.

As shown, bevels 30, andfil maybe provided in the, leading edge of eachrtongue for both attaining greater; extension of each tongue into each groove and providing; clearance for the vapor impervious strip. V-shapedI grooves. 32 may also be provided betweenv lower edges. of' adjoining units.

Continuous vapor impervious film 14inter-mediatethe. insulating-boards can be formed of adhesive or nonadhesive water vaporv impervious or substantially. im-,

pervious material, e.g. asphalt, pitch, polyethylene, aluminum, cellulose acetate, a' plasticized polyvinyl chlorid composition hereinafter described, polyester film or rubber-like materials. While not necessary to successful practise. of the invention, itis oftenldesirable to support or bond such film, particularly when formed ofnonadhesive material, between paper sheets, which papercovered film can be relatively easily bonded-tothe insulating boards usingconventional aqueous adhesive. How'- ever, his to be understood that a non-adhesive film not covered with paper. could be bonded directly to the boards, if desired, with any suitableadhesive material. Excellent resultshave'been obtained when film 14 is a compositioncontaining, by weight, polyvinyl chloride 40-60%,

pitch. 30-40%. and dioctyl phthalate 15-20% (the pitch and phthalate being plasticizers), and this film (typically 4hmils thick) is'bondedior calenderedbetweentw'o paper 5 eets;

The upper and; lower boards 11 and 12 respectively of each roof deck element or unit are typically conventional wood. fiber insulating boards. Thezupper boards may be impregnated with asphzdtwhile the lower boards, which provide the exposed decorativesurface, are gen-. erally notgimpregnated. If desired, the boards'could be fabricated or made ofother fibrous insulatingmaterial such as Wood pulp, bagasse, fiax'straw or ground wood.

With reference now to FIGURE 2, a roof deck element or unit 33 of this-invention is-provided with tongues 3.4i and 350m a. longitudinal. and transvers'eedge and grooves 35 and 37 on a transverse and longitudinal edge. The unit has typical width and length of 2 and 8' respectively and thickness of 2"3". Vapor impervious strips of, for example, the plasticized chlorinated rubber or other water vapor impervious material previously mentioned are bonded in grooves 36 and 37 to contact and cover normally exposed asphalt or other vapor impervious film edges as previously discussed. If desired, the tongues may extend only from the longitudinal edges of the roof deck, and the transverse edges thereof may be fiat or non-grooved to form butt joints on assemblage thereof with similar units. However, use of these last mentioned units is less preferred because the butt joints have to' be caulked with a caulking material to provide vapor barrier continuity through the joint, 9. time consuming and sometimes troublesome operation. On the contrary, automatic vapor barrier continuity through the tongue and groove joints is attained by the vapor impervious strips installed or bonded in the grooves of the units. The roof deck units are usually assembled on the rafters or cross beams in a manner such that the afore mentioned V-shaped grooves (between adjoining units) are perpendicular to the rafters or beams. However, the units may be assembled on the rafters in any desired manner.

As shown in FIGURE 3, normally exposed vapor impervious film edge 33 in groove 36 is intermediate upper and lower insulating boards 39 and 41} respectively. Vapor impervious "1p 41 of soft rubber or other vapor impervious material previously mentioned is bonded by application of any suitable adhesive material to the groove bottom, and contacts and covers film edge 34. if the strip is formed of adhesive material such as the plasticized chlorinated rubber composition previously mentioned,

adhesive material is obviously not required for effecting a such bonding. While the strip is preferably installed or bonded to the groove bottom at the factory, installation may be efiected at the job site. The strip may be installed as such, or by employment of a suitable mold vhen the vapor impervious material is in fiowable or liquid state. This latter installation is particularly desirable when the vapor impervious material is the aforementioned plasticized chlorinated rubber composition or an asphalt or pitch compound.

On joining or engaging the unit with other similar units, rubber strip 41 contacts and covers the exposed film edge at the leading tongue edge of the adjoining unit thereby automatically forming a continuous and sealed vapor barrier between adjoining units.

With reference now to FIGURE 4, two joined or engaged insulating roof deck units have similar structure as two engaged units of the roof deck structure of FIG- URE 1. However, in the FEGURE 4 embodiment, compressible, vapor impervious strip 4-2 of rubber or other aforementioned vapor impervious material is seated in and extends the length of a groove or rabbet 43 and projects outwardly therefrom. Strip 42 contacts and covers at the rabbet bottom the normally exposed film edge 44 of film 45, which is formed of the previously mentioned plasticized polyvinyl chloride composition calendered between paper sheets 46 and 47, the sheets being bonded to the insulation by means of applied adhesive material. The strip also contacts and covers normally exposed film edge 48 (of a similar paper covered vapor impervious film) at the leading tongue edge or" the adjoining unit, whereby a continuous and sealed vapor barrier is automatically provided between the units.

Rabbet as, which is of substantially identical or similar length and of lesser width than the length and width respectively of the main groove, is advantageous because it serves both as means for anchoring or firmly fixing the preferably factory-installed strip 42, and to protect the strip during shipping and handling. For instance, the width of the rabbet d2 may be slightly less than that of the com ressible rubber strip and the strip compressed and then forced into the rabbet whereby the strip is held firmly therein. If desired, the rabbet width may be slightly greater than that of strip 37 and the strip bonded, if formed of non-adhesive material, to the upper and low er faces of the rabbet with any suitable adhesive material.

As shown in FIGURE 5, four tongued and grooved insulating roof deck units 49, 50, 51 and 52, each of structure similar to the unit of FIGURE 2, are engaged edge to edge through tongue and groove joints. Vent channels 53, 54, 55, 56, 57 and 58 are located in the groove bottoms of the units. As shown, vent channel 58 of unit 52 communicates with channel 56 of adjoining unit 51 to vent transversely of the units destructive pressures built up within the engaged units. Similarly, vent channel 53 of unit 49 communicates with vent channel 57 of unit 52 to vent longitudinally destructive pressures built up within the units. Vent channels 56 and 58 would of course communicate transversely with vent channels of other adjoining units, and vent channels 53, 54, 55 and 57 would communicate longitudinally with vent channels of other adjoining units to vent destructive pressures from the units.

As more fully described in copending applications Serial No. 482,168, filed January 17, 1955, now Patent No. 2,833,229 and Serial No. 555,966, filed December 28, 1955, now Patent No. 2,849,018, vent conduits provided with unidirectional check valves, e.g. tubular rubber exhalation or ball check valves, may be so disposed in the insulating structure as to communicate the intercommunicating vent channels with either the interior or exterior of the building thereby to complete venting of destructive pressures. Alternatively, if desired, the intercommunicating vent channels can vent the pressures exterior of the bui ding through edge vent holes or orifices located at the roof edge or parapet.

Although certain preferred embodiments of the invention have been disclosed for purpose of illustration, it will be evident that various changes and modifications may be made therein without departing from the scope and spirit of the invention.

What is claimed is:

1. An insulating roof deck structure composed of insulating units, the insulating units comprising a pair of superposed fibrous insulating boards having a film of vapor impervious material coextensive with and sandwiched between the entire face to face surfaces of the superposed fibrous boards, adjoining units of the roof deck structure joined by tongue and groove joints on the opposite sides of the units respectively with the film of vapor impervious material terminating in film edges at edges of the units within the tongue and groove joints, the tongues of the insulating units having horizontal, parallel, opposite upper and lower faces, the grooves of the insulating units having a horizontal lower face flush with the lower face of the tongue and an upper face inclined upwardly and outwardly of the unit, said grooves being of lesser width in the region adjacent the groove bottom than the normal width of said tongues with the forward edge of the upper surface of the tongues firmly impressed against the inclined upper surface of the grooves, a strip of vapor impervious material compressed in the lower bottom corner of the groove between the lower forward ends of the tongues and the lower bottom corner of the grooves and covering the entirety of each of the film edges of adjoining units within the joints, said strip of vapor impervious material running the full length of the grooves and terminating at the ends thereof in contact with similarly disposed strips in the grooves of adjoining units forming a continuous and sealed barrier between adjoining units against passage of vapor from one side of the barrier to the other side, and a vent channel of lesser width than that of the grooves and extending the length thereof in the groove bottoms of each insulatpor impervious materialcoextensive withand sandwiched betweenthe entire face to face surfaces of. the superposed fibrous boards, adjoiningunits of the roof deck structure joined by tongue, and groove joints 0n the opposite sides of: the units respectively with the film of vapor impervious: material terminating in film edges along lower bevelled edges ofthe, tonguesand within the grooves,

the tongues of the insulating, units .having horizontal, 1 paralleL, oppositeupper andrlower faces, said upper face terminating. in a. bevel, the grooves of the insulating units having a horizontal lower-facetfiush with .thelower face oi the tongue and anupper face inch'nedupwardly and; outwardly of theiunit, saidgrooves being of 'lesserawidth in the region adjacentthe groove bottom than the normal' width'of said tongues withthe upper edgeofsaid upper" forward bevel of the tongues firmly impressed; against the-inclined upper surface of the grooves, a strip of vapor impervious, material. compressed in the lower, bottom corner. ()f'iihfi' grooves between the'lower bevelled forward end ofthe tongues and the lower bottom corner frthe. groovestand coveringthe entirety of each of the ,filmedges of adjoining units within the joints, said stripv joiningrunits forming, a continuous and sealed barrier between adjoining units against passage ofvapor fronts one side of the barrier to theother side, anda vent' channel of lesser width than that of the grooves and extending the length thereof in thegroove bottoms of each insulating unit and spaced above the vaponimpervious filmedge therein, said vent channel communi eating with similar vent channels in adjoining unitsjto V vent destructive pressures builtup Within the adjoining units,v

References Cited in the file of this patent UNITED STATES PATENTS- 4G8g066- Beaumont July 30, 1889' 502,289 Feldmann- Aug. 1, 1893 1,083,243 Edwards -Dec. 30,1913 1374;082 Hedges Apr. 5, 1921 1,863,231 Thune- June '14, 1932 2,152g694 Hoover Apr. 4, 1939 2,192,458 Swenson et al; a Mar. 5, 1940 2,390,087 Fink- Dec. 4, 1945 2,872,882" Paul -1 Feb. 10, 1 959 2,887,426 Knold May 19;1959

FOREIGN PATENTS 248,515 Great Britain' Mar. 11, 1926 124,957 Switzerland Apr; 2, 1928' 168,141 Austria Apr..25, 1951 507,299. Canada Nov. ,16, 1954'.

OTHER REFERENCES Architectural Record of May 1954, pages 216, 217-.

:UNITED STATES PATENT OFFICE CERTIFICATE OF CDRBECTION Patent No, 3,079,730 March 5, 1963 Joseph W, Donegan It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as.

corrected below.

In the grant, lines 2 and 3, for "assignor to Allied Chemical 81 Dye Corporation, of New York, N Y, a corporation of New York" read assignor to Allied Chemical Corporation, a corporation of New York line 12, for "Allied Chemical 8: Dye Corporation, its successors" read Allied Chemical Corporation, its successors in the heading to the printed specification, lines 5 to 7, for "assignor to Allied Chemical 81' Dye Corporation, New York, N, Y, a corporation of New York read assignor to Allied Chemical Corporation, a corpora? tion of New York Signed and sealed this l9thday of November 1963.,

(SEAL) Attest:

ERNEST W. SWIDER EDWlN L, REYNOLDS Afiesiillg Officer Ac ting Commissioner of Patents 

1. AN INSULATING ROOF DECK STRUCTURE COMPOSED OF INSULATING UNITS, THE INSULATING UNITS COMPRISING A PAIR OF SUPERPOSED FIBROUS INSULATING BOARDS HAVING A FILM OF VAPOR IMPERVIOUS MATERIAL COEXTENSIVE WITH AND SANDWICHED BETWEEN THE ENTIRE FACE TO FACE SURFACES OF THE SUPERPOSED FIBROUS BOARDS, ADJOINING UNITS OF THE ROOF DECK STRUCTURE JOINED BY TONGUE AND GROOVE JOINTS ON THE OPPOSITE SIDES OF THE UNITS RESPECTIVELY WITH THE FILM OF VAPOR IMPERVIOUS MATERIAL TERMINATING IN FILM EDGES AT EDGES OF THE UNITS WITHIN THE TONGUE AND GROOVE JOINTS, THE TONGUES OF THE INSULATING UNITS HAVING HORIZONTAL, PARALLEL, OPPOSITE UPPER AND LOWER FACES, THE GROOVES OF THE INSULATING UNITS HAVING A HORIZONTAL LOWER FACE FLUSH WITH THE LOWER FACE OF THE TONGUE AND AN UPPER FACE INCLINED UPWARDLY AND OUTWARDLY OF THE UNIT, SAID GROOVES BEING OF LESSER WIDTH IN THE REGION ADJACENT THE GROOVE BOTTOM THAN THE NORMAL WIDTH OF SAID TONGUES WITH THE FORWARD EDGE OF THE UPPER SURFACE OF THE TONGUES FIRMLY IMPRESSED AGAINST THE INCLINED UPPER SURFACE OF THE GROOVES, A STRIP OF VAPOR IMPERVIOUS MATERIAL COMPRESSED LOWER FORWARD ENDS OF THE TONGUES AND THE LOWER BOTTOM CORNER OF THE GROOVES AND COVERING THE ENTIRETY OF EACH OF THE FILM EDGES OF ADJOINING UNITS WITHIN THE JOINTS, SAID STRIP OF VAPOR IMPERVIOUS MATERIAL RUNNING THE FULL LENGTH OF THE GROOVES AND TERMINATING AT THE ENDS THEREOF IN CONTACT WITH SIMILARLY DISPOSED STRIPS IN THE GROOVES OF ADJOINING UNITS FORMING A CONTINUOUS AND SEALED BARRIER BETWEEN ADJOINING UNITS AGAINST PASSAGE OF VAPOR FROM ONE SIDE OF THE BARRIER TO THE OTHER SIDE, AND A VENT CHANNEL OF LESSER WIDTH THAN THAT OF THE GROOVES AND EXTENDING THE LENGTH THEREOF IN THE GROOVE BOTTOMS OF EACH INSULATING UNIT AND SPACED ABOVE THE VAPOR IMPERVIOUS FILM EDGE THEREIN, SAID VENT CHANNEL COMMUNICATING WITH SIMILAR VENT CHANNELS IN ADJOINING UNITS TO VENT DESTRUCTIVE PRESSURES BUILT UP WITHIN THE JOINED UNITS. 